Power is an interesting topic with filters and that interest turns to concern when the filter must operate at high altitudes. This post is not a comprehensive research paper; it is just a brief discussion of the thought behind designing filters for high-altitude use.
RF power will be “effectively greater” at high altitudes than at sea level due to the lack of atmosphere to absorb the RF energy. I say “effectively greater” because the power at high altitude is not greater in Watts than at sea level, but when the effect of high altitude is considered, one must design a filter for a higher power rating than at sea level. Simply put, 100 W at high altitude behaves differently in a filter than 100 W at sea level.
The main concern is the Corona effect – some will call it arcing, which can happen inside a cavity filter. This effect can be more pronounced at high altitudes because the atmosphere’s density is much lower at these altitudes and the charged particles in the atmosphere are freer to interact with the magnetic fields generated in the filter. However, at sea level, the Earth’s atmosphere is much denser, which can dampen the interactions between the charged particles and the magnetic field, leading to a less pronounced (or nearly non-existent) Corona effect.
Generally speaking, a greater distance must be created between the tuning elements and the resonators to account for the power effect at high altitude. This distance must be such that the gap between the two is sufficiently large enough to prevent arcing across it. There are various methods to calculate the space required and it is wise to add a little extra margin to account for the unexpected. Once the hurdle of designing for power at altitude is cleared, the rest of the design will fall into place quite easily.
Reactel has extensive experience designing high-power filters and multiplexers at extreme altitudes.
Don’t hesitate to contact us if you are looking for a unit for this environment.